1. Field of the Invention
The present invention relates to a liquid level detector and a liquid level measuring apparatus of a printer adopting the same and, more particularly, to a detector for detecting the level of liquid contained in a container in a non-contact manner and a liquid level measuring apparatus of a printer adopting the same.
2. Description of the Related Art
An apparatus for measuring the level of liquid contained in a container is adopted to a liquid development type printer such as a laser printer or copying machine using ink as developer. The liquid level measuring apparatus provides information about the amount of ink stored in the container. The information about the remaining amount of ink provided by the liquid level measuring apparatus adopted to a printer is used to prevent the printer from running out of ink. Since the ink supply can be managed by adopting the liquid level measuring apparatus, incomplete printing or interruption of printing due to running out of ink can be avoided.
In the conventional optical liquid level measuring apparatus, a light source and a photodetector are provided so that the light source emits light toward a container of liquid and the amount of light reflected or passing through the container is detected to measure the level of the liquid. However, the optical liquid level measuring apparatus may cause an error in measuring the level of liquid due to ink adhering to and solidified on an inner wall of the container.
In another example of the conventional liquid level measuring apparatus, a float is installed in a container of liquid, and the vertical displacement of the float is detected to measure the level of the liquid. However, since the specific gravity varies with the liquid being measured, the float needs to be manufactured according to the specific gravity of the developer.
Also, there is another method in which two electrode plates are installed inside a container such that the liquid level is measured from the measured change in electrostatic capacity which corresponds to the change of the level of liquid contained between the two electrode plates. However, since toner often adheres fixedly to the electrode plates regardless of the change of the liquid level, an error may be generated when the liquid level is measured.
To solve the above problems, it is an object of the present invention to provide a liquid level detector which can accurately measure the level of liquid stored in a container from outside of the container, and a liquid level measuring apparatus of a printer adopting the same.
Accordingly, to achieve the above object, there is provided a liquid level detector comprising an electrode portion including a substrate, a first electrode plate, which is separated a predetermined distance from the substrate by a support bar, a hollow second electrode plate extending from the substrate to the first electrode plate and having an opening corresponding to the outer circumferential surface of the first electrode plate, and a liquid level detecting portion which detects the presence of the liquid at the detection position from a change in electrostatic capacity measured by the first and second electrode plates.
Also, to achieve the above object, there is provided a liquid level measuring apparatus of a printer which comprises a plurality of liquid level detectors, installed outside a container for storing liquid to be supplied to a developing apparatus of the printer at liquid level detecting positions set at predetermined intervals in a vertical direction, which detect a change in electrostatic capacity according to the presence of the liquid and output a corresponding signal, and a controller which controls each of the liquid level detectors so that the operation time of each of the liquid level detectors does not overlap, and which determines the level of the liquid stored in the container from the signal output from each of the liquid level detectors.